Compressors for refrigerating machine disposing a compressing mechanism within an enclosed container, or so-called enclosed type compressors are roughly classified into rotary type, reciprocating type, and scroll type. In any part, in the area exposed to the refrigerant, there is a contact portion in which metal members contact with each other. The vanes and pistons are formed of various materials such as cast iron and aluminum alloy.
On the other hand, in the refrigerants used hitherto, such as chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), for example, CFC11, CFC12, HCFC22, chlorine atoms are contained in molecules, and the chlorine is known to induce depletion of ozone layer, and substituent refrigerants are being developed and used.
Highly practicable substituent refrigerants include chlorine-free hydrofluorocarbons (HFCs) (Hydraulic and Pneumatic Technology, No. 6, 1994, published by Nippon Kogyo Shuppan).
When using such substituent refrigerants, for example, R134a, R125, R32, since the substituent refrigerants do not contain chlorine which has an extreme pressure effect, such lubricity as recognized in the conventional designated CFCs and designated HCFCs is not expected. Accordingly, the contact condition becomes severe, and the oil film may be partly broken in the contact area, and a boundary lubrication state is likely to occur. In this area of boundary lubrication state, sticking occurs between both contact members in the contact area to cause early wear or seizure, which leads to lowering of refrigerating performance and decline of reliability. In the compressor for refrigerating machine of the conventional rotary type, abrasion is extreme between the tip of the vane and the outer periphery of the piston.
The lubricating oil as the refrigerating machine oil when using such substitute refrigerant is particularly required to have compatibility of refrigerant and lubricating oil, from the viewpoint of lubrication for bringing in and supplying the lubricating oil into parts of the compressor by the flow of refrigerant and from the viewpoint of efficiency of heat exchange. When using conventional refrigerants such as CFCs and HCFCs, mineral oil or alkyl benzene was widely used as lubricating oil, but such lubricating oil is extremely poor in compatibility with such substitute refrigerant, and it has been considered to use ester compound oil having compatibility with substitute refrigerant (Hydraulic and Pneumatic Technology, No. 6 , 1994, published by Nippon Kogyo Shuppan).
However, since the ester compound oil has a polar group and is high in moisture absorption, the absorbed moisture decomposes the ester compound oil to produce carboxylic acid. This carboxylic acid corrodes the surface of the contact members, and lowers the fatigue reliability of the contact members (Hydraulic and Pneumatic Technology, No. 6, 1994, published by Nippon Kogyo Shuppan). Moreover, by decomposition of ester compound oil, hydrogen is produced, and this hydrogen invades into the contact members to cause hydrogen brittleness or stress corrosion, which results in decline of reliability of contact members. The ester compound pound oil also produces metal soap by hydrolysis and forms sludge, and this sludge clogs the capillary tube to cause adverse effects on the refrigerating cycle.
To solve such problems, it may be considered to add proper additives to the lubricating oil for preventing such undesired reaction and enhancing the lubricity of the contact area. Despite various studies, sufficient effects are not obtained, and further improvements are expected.
It is hence an object of the invention to solve such problems and present a compressor for refrigerating machine having a high refrigerating performance and an extremely high reliability.